Nutrient dynamics in the La Romaine river and reservoir complex
Reservoirs can alter the transport and export of nutrients and organic matter from rivers to estuaries. In the La Romaine River, a series of four hydroelectric dams have been progressively built between 2015 and 2019 where we have been able to monitor the river through this progression and aging process. Here, we present longitudinal patterns in concentrations of total nitrogen (TN), total phosphorous (TP), dissolved organic carbon (DOC), and stoichiometric ratios (C:N:P) within the La Romaine River and reservoirs. We found that the reservoirs can be both sources and sinks of N, but concentrations below the dams remained on average roughly similar to those in the upstream river. TP concentrations, in contrast, consistently increased longitudinally and were grater below the dams than upstream, suggesting that the reservoirs are net sources of P. DOC concentrations were relatively constant across the river and the reservoir continuum. Stoichiometric ratios varied longitudinally where N:P decreased from above the reservoirs to the estuary, C:N were relatively constant, and C:P declined through the reservoirs and downstream river into the estuary; these stoichiometric shifts were mostly driven by changes in P concentrations. Our data suggest that in these young boreal reservoirs can be sources of nutrients, with P playing a major role in biogeochemical processes. Continuous monitoring is needed to determine how and if these signals will vary with age of reservoirs.
Bianca Rodríguez-Cardona, Pascal Bodmer, Felipe Rust, Masumi Stradler and Paul del Giorgio
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